This invention relates, in general, to extracoronal attachments for a removable partial denture and more particularly to the attachment and to a method and kit for use in constructing and applying such attachment.
The invention is particularly applicable to dentures having a free unilateral or bilateral end and will be described with particular reference thereto. However, it will be appreciated by those skilled in the art that the invention may have broader applications and may be applicable to other dental applications involving pontics or a bridge requiring or utilizing a joint-type attachment.
Where several posterior teeth must be replaced and the remaining teeth within the oral cavity cannot support a fixed partial denture, it is often desirable to use a removable partial denture. In order that the denture be retained in position while in use in the wearer's mouth, the partial denture must be anchored in some manner within the mouth generally by being removably attached to the abutment teeth, i.e. the anterior teeth closest to the removable bridge.
There are two basic types of anchoring attachments in use. The first type includes extracoronal attachments on a denture, such as clasps, which are used to grip around the abutment teeth. In fact, the clasps tightly grip the abutment teeth to maintain a firm connection between the partial denture and abutment teeth and while functionally acceptable, the clasps are visible and unsightly and render a particularly unsatisfactory cosmetic appearance. As an alternative to such extracoronal attachment, many different types of intracoronal and extracoronal attachments have been proposed and are in use.
One such type of extracoronal device is marketed under the commercial name "PRECI-VERTIX" which uses a male retainer attached to the abutment tooth and a female retainer embedded in the denture. More particularly, a burnout plastic male pattern in the shape of a cylindrical rod can be accurately formed and then applied to the crown pattern of the abutment tooth. The female retainer which is fitted within the denture has a slotted cylindrical opening in turn fitted with a slotted plastic, resilient sleeve to receive the male retainer to provide a precision attachment. A similar type of extracoronal attachment is marketed under the name "STERN .RTM.JMS SYTEM" (Jacket Maintenance System) in which the female retainer is mounted within the crown of the abutment tooth and the male retainer applied to the denture. In this arrangement the full length plastic insert has a trapezoidal cross-sectional opening to receive the similarly shaped male retainer. A third extracoronal joint is marketed under the name "DALBO". In this arrangement the male retainer is attached to the abutment tooth and has a spherical ball protruding from the abutment tooth adjacent the gingival margin. The female retainer has a slotted cylindrical opening and is embedded in the denture. Within the cylindrical opening is a stiff spring which resists vertical movement of the male sphere relative to the denture. In each of the arrangements discussed, the joint formed by the male and female retainers is under significant stresses in tension and compression during normal use of the denture. This requires that one of the retainers, male or female, be securely anchored to the abutment teeth and all such attachments have heretofore required the construction of a crown over the abutment tooth. To make such a crown requires that an otherwise healthy tooth be ground down and reduced in size so that a crown containing the appropriate connected member may be cemented on the remains of the tooth to support the connected member and replace, cosmetically and functionally, the now-destroyed tooth.
Other alternative arrangements for mounting pontics have been employed which do not destroy the abutment tooth. It is known that satisfactory results have been achieved by means of a resin-bonding technique for fixed partial dentures or for a tooth replacement which is known conventionally as the Acid Etched Resin Bonded Retainer Technique. This technique, incorporated by reference herein, uses an acid etch in combination with a slight modification of the abutting teeth to resin bond the framework supporting the pontic or fixed bridge to the enamel of the abutting teeth. A close review of the retainer designs utilized with such technique disclose that the biting or functional loading forces place the retainer design primarily in compression with little tensile or shear stresses exerted on the retainer. The removable intracoronal and extracoronal precision attachments discussed above all produce significant shear and tensile stresses on the retainers which, it is believed, will not produce an acceptable, long lasting attachment, if the retainer was simply resin bonded to the abutment teeth.